fix: use InMemoryCatalog to avoid config collision in tests

[geruh]

Rationale for this change

Fixes a test failure that hits anyone with PyIceberg already configured.

The test uses load_catalog("default", type="in-memory"), which merges your dev environment config with the test parameters. If you have a default catalog defined in ~/.pyiceberg.yaml with something like uri: https://best-rest-catalog.com, the merge produces {"uri": "https://best-rest-catalog.com", "type": "in-memory"}. SQLAlchemy sees that https:// URI and tries to load it as a database dialect, which fails wuth:

sqlalchemy.exc.NoSuchModuleError: Can't load plugin: sqlalchemy.dialects:https

Therefore, this PR avoids using the local pyicberg.yaml file entirely!

Are these changes tested?

Yes. I created a conflicting ~/.pyiceberg.yaml with a default catalog pointing to an HTTPS REST endpoint, confirmed the old code fails, and verified the fix bypasses the config merge and works.

Are there any user-facing changes?

No

[nssalian]

looks good just want to make sure this doesn't break nightly builds or something else. @kevinjqliu might be able to trigger one

[rambleraptor]

Really clever find! Do we want to consider having some kind of load_catalog method that purposefully doesn't do this? This feels like something that could pop up again on an unrelated test.

[kevinjqliu]

thanks for catching this! ideally we shouldn't let external factors (such as the content of ~/.pyiceberg.yaml) affect the test suite; that pollutes the tests imo.

i remember we disables parsing the env and config file here

iceberg-python/tests/cli/test_console.py

Lines 40 to 42 in 7e66ccb

	# mock to prevent parsing ~/.pyiceberg.yaml or {PYICEBERG_HOME}/.pyiceberg.yaml
	mocker.patch.dict(os.environ, values={"HOME": empty_home_dir_path, "PYICEBERG_HOME": empty_home_dir_path})
	mocker.patch("pyiceberg.catalog._ENV_CONFIG", return_value=Config())

perhaps we can do this as the default for all tests

[geruh]

Yeah, local config shouldn't bleed into pytest runs. The better fix is in the test infra rather than patching individual tests.

I added a session-scoped autouse fixture in the root conftest that replaces _ENV_CONFIG with a fresh Config() that skips file loading. Env vars still work for CI. This way load_catalog is safe to use in tests without worrying about config leaking in.

Did a sanity test-coverage run and everything looks goood!!!